Abstract
The study of CMRP (Cobalt-mediated radical polymerization) has been developed rapidly. Here, we synthesized a half-salen type bidentate ligand to chelate cobalt(II) metal. This novel cobalt complex we called CoII(half-salen*) differed from CoII(salen*) in its structure but same in its composition. The structure of CoII(half-salen*) was similarly tetrahedral while the structure of CoII(salen*) was square planar. Due to CoII(salen*) have been applied in CMRP of vinyl acetate successfully that might indicate CoII(half-salen*) also have potential to mediate radical polymerization of vinyl acetate. The polymerization was initiated by either heat or light. In thermo-initiation, the control of CoII(half-salen*) could be improved via reducing temperature or increasing the ratio of initiator. At low temperature, the molecular weight was higher than theoretical molecular weight and the PDI value was large (PDI = 1.62-1.72) in CMRP. To improve the control of CoII(half-salen*), the CMRP was carried out under 365 nm irradiation with photo-initiator of TPO. As the ratio of initiator rose, the molecular weight would fit theoretical molecular weight more closely. However, it occurred chain transfer reaction during polymerization servely with low light intensity and high ratio of initiator in polymerization. As light intensity was high, the molecular weight fit the theoretical molecular weight better with low ratio of initiator. However, higher light intensity gave higher PDI value. To lower the PDI value, we have tried to change the temperature during the polymerization. The PDI values reduced as we increased temperature, however, the molecular weight deviated from the theoretical molecular weight at the same time.